Method and apparatus for manufacturing fine particles

ABSTRACT

An apparatus for manufacturing fine particles includes a reactor; a first inlet part including at least one port introducing a reactive gas flow containing a fine particle source material; a second inlet part including at least one port introducing a diluting gas flow; a heater exciting the fine particle source material in the reactive gas flow; a first plate including through-holes which substantially equalize a flow rate of the reactive gas flow with respect to a cross section of a flow channel; a second plate including through-holes which substantially equalize a flow rate of the diluting gas flow with respect to a cross section of a flow channel; a gas exhaust port provided in a merging region where the reactive gas flow passed through the first plate and the diluting gas flow passed through the second plate are merged; and a collector which collects fine particles.

CROSS REFERENCE TO RELATED APPLICATION

The present divisional application claims the benefit of priority under35 U.S.C. §120 to application Ser. No. 10/242,634, filed on Sep. 13,2002, and under 35 U.S.C. §119 from Japanese Patent Application No.2001-292279 filed on Sep. 25, 2001, the entire contents of both areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for manufacturing fineparticles and to apparatuses for manufacturing fine particles. Morespecifically, the present invention relates to a vapor-phase growthmethod for fine particles in nanometer sizes and to a manufacturingmethod thereof.

2. Description of the Related Art

Fine particles in nanometer sizes exert unprecedented functions due to aquantum size effect. Accordingly, fine particles are recently drawingattention as new substances. Depending on types of materials, such fineparticles are applied to fluorescent materials for visible light LEDelements and displays, magnetic recording media and the like.

In general, fine particles are fabricated by use of a vapor-phase growthmethod. FIG. 1 is a view showing a constitution of a conventionalapparatus for manufacturing fine particles. For example, ZnS fineparticles being fluorescent materials are manufactured in accordancewith the following method by use of the apparatus shown in FIG. 1(Okuyama et al. J. Materials Science, vol. 32, 1229-1237 (1997)).

Source gas containing Zn(NO₃)₂ and SC(NH₂)₂ is introduced into a reactor101, in which it is adjusted to a normal pressure inert gas atmosphere,and heated up to a range from 600° C. to 700° C. with a heater 102provided on the reactor 101. The source gas heated causes a chemicalreaction as defined in the following formula (FI), thus ZnS fineparticle cores are generated.Zn(NO₃)₂+SC(NH₂)₂→ZnS+2NO+CO₂+N₂+2H₂O  (FI)

The ZnS fine particle cores grow larger in the process of moving insidethe reactor. The ZnS fine particles thus obtained are discharged fromthe reactor 101 together with other gas and diluted with inert gas onthe way, then the ZnS fine particles and the inert gas are introduced toa cooling device 103 and cooled down to a room temperature.

The cooled gas containing the generated fine particles passes through acollector 104 filled with a solution containing a surfactant. Thus, onlythe generated particles are collected in the solution and preserved in adispersed state.

FIG. 2A and FIG. 2B are graphs concerning the above-describedvapor-phase growth method, which show variations in the number ofgeneration and sizes of fine particles with respect to reactive timestarting from the time when the source gas is introduced into thereactor 101 and a fine particle generating reaction is initiated.

As shown in FIG. 2A, the number of generation of the fine particlesincreases constantly in the beginning with passage of time. However, thenumber of generation is saturated after 0.001 second or thereabout, andthen the number of generation gradually decreases thereafter with time.After a lapse of 0.1 second, the degree of decrease in the number ofgeneration of the fine particles is significantly accelerated.

In the meantime, as shown in FIG. 2B, an average particle size scarcelychanges for 0.001 second or thereabout when the number of generation ofthe fine particles is constantly increasing. However, the average grainsize starts increasing with passage of time after 0.001 second orthereabout when the number of generation of the fine particles issaturated.

Based on these data, it is conceivable that growth of the fine particlesproceeds with the following three stages (I to III) according to theparticle growth method using the conventional vapor-phase growth method.

First stage (I): The source gas is decomposed and the fine particlecores (molecules) are generated as seeds of particle generation. In thisprocess, although the number of the fine particles increases, the fineparticle sizes scarcely change (A fine particle core generatingprocess).

Second stage (II): The generated fine particle cores are bonded togetherin a range from several to several hundred particles and grow intoclusters in nanometer sizes. Therefore, at this stage, the number ofgeneration of the fine particles decreases with passage of time;meanwhile, the fine particle sizes start increasing (A fine particlecluster generating process).

Third stage (III): The clusters generated in nanometer sizes cohere toform fine particles in sizes of 10 nanometers or larger. Accordingly,the number of generation of the fine particles decreases further (Acluster cohering process).

Among the above-described three stages, generation of the fine particlecores in sizes of 10 nanometers or below suitable for exerting a quantumeffect progresses most efficiently during the first stage. However, asshown in FIG. 2A and FIG. 2B, the first stage ends in an extremely shortperiod as the first stage lasts only for 0.001 second at the longestfrom initiation of the fine particle generating reaction. When theconventional vapor-phase growth method is applied, it is impossible tocontrol the reactive time in a range within 0.1 second. Accordingly, thegrowth of the fine particles progresses toward the third stageinevitably. As a result, as shown in FIG. 3, the obtained fine particlesinclude a considerable number of fine particles larger than 10nanometers.

Therefore, in order to obtain the fine particles in the sizes within 10nanometers which exert the quantum effect, required is an additionaloperation for extracting only the fine particles in a predetermined sizerange by use of a classifier out of the fine particles collected andpreserved in accordance with the conventional manufacturing method. As aresult, additional costs are involved upon manufacturing the fineparticles.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method capable ofmanufacturing fine particles in sizes within 10 nanometers without arequirement of classification, and to provide an apparatus formanufacturing fine particles for use in the manufacturing method.

In a first aspect of the method of manufacturing fine particlesaccording to the present invention, a reactive gas flow containing afine particle source material is introduced into a reactor from oneside, and then fine particles are grown in a gas phase by heating in thereactive gas flow. Meanwhile, a diluting gas flow is introduced into thereactor from the other side, which is almost counter-flow to thedirection of the reactive gas flow. Further, flow rates of the reactivegas flow and the diluting gas flow with respect to a cross section of aflow channel are severally equalized substantially, and then thereactive gas flow and the diluting gas flow are merged so as to stopgrowth of the fine particles.

In a second aspect of the method of manufacturing fine particlesaccording to the present invention, a reactive gas flow containing afine particle source material is introduced into a reactor from oneside, and a diluting gas flow is introduced from the other side beingalmost counter-flow to the reactive gas flow. While the reactive gasflow and the diluting gas flow are merged, the fine particle sourcematerial is excited to grow fine particles in such a merging region andthe growth of the fine particles is stopped by dilution owing to thediluting gas flow.

A first aspect of an apparatus for manufacturing fine particlesaccording to the present invention includes a reactor, a first inletpart provided on one side of the reactor, which has at least one portintroducing a reactive gas flow containing a fine particle sourcematerial, a second inlet part provided on the other side in the reactorbeing approximately counter-flow to the side of the first inlet part,which has at least one port introducing a diluting gas flow, and aheater which excites the fine particle source material contained in thereactive gas flow. In addition, the apparatus further includes a firstplate disposed inside the reactor almost perpendicularly with respect tothe reactive gas flow and having through-holes which substantiallyequalize a flow rate of the reactive gas flow with respect to a crosssection of a flow channel, and a second plate disposed inside thereactor almost perpendicularly with respect to the diluting gas flow andhaving through-holes which substantially equalize a flow rate of thediluting gas flow with respect to a cross section of a flow channel.Furthermore, the apparatus further includes a gas exhaust port providedin a merging region where the reactive gas flow passing through thefirst plate and the diluting gas flow passing through the second plateare merged, and a collector which collects fine particles contained inthe gas discharged from the gas exhaust port.

A second aspect of the apparatus for manufacturing fine particlesaccording to the present invention includes a reactor, a first inletpart provided on one side of the reactor, which has at least one portintroducing a reactive gas flow containing a fine particle sourcematerial, a second inlet part provided on the other side of the reactorbeing approximately counter-flow to the side of the first inlet part,which has at least one port introducing a diluting gas flow, a plasmagenerator which generates plasma in a merging region where the reactivegas flow and the diluting gas flow are merged, a gas exhaust portprovided adjacently to the merging region, and a collector whichcollects fine particles contained in the gas discharged from the gasexhaust port.

A third aspect of the apparatus for manufacturing fine particlesaccording to the present invention includes a reactor, a first inletpart provided on one side of the reactor, which has at least one portintroducing a reactive gas flow containing a fine particle sourcematerial, a second inlet part provided on the other side in the reactorbeing approximately counter-flow to the side of the first inlet part,which has at least one port introducing a diluting gas flow, a heaterwhich heats the diluting gas flow, a gas exhaust port provided in amerging region where the reactive gas flow and the diluting gas flow aremerged, and a collector which collects fine particles contained in thegas discharged from the gas exhaust port.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a constitution of a conventional apparatus formanufacturing fine particles.

FIG. 2A is a graph showing the relation between reactive time and thenumber of generation of fine particles in the case of using aconventional method of manufacturing fine particles, and FIG. 2B is agraph showing the relation between the reactive time and averageparticle sizes in the case of using the conventional method ofmanufacturing fine particles.

FIG. 3 is a graph showing distribution of particle sizes of the fineparticles obtained in accordance with the conventional method ofmanufacturing fine particles.

FIG. 4 is a constitutional view showing an apparatus for manufacturingfine particles according to a first embodiment of the present invention.

FIGS. 5A to 5D are perspective views showing examples of gas-flowcontrolling plates for use in the apparatus for manufacturing fineparticles according to the first embodiment.

FIG. 6 is a graph showing a result of simulation of temperaturedistribution in a gas merging region when a gas-flow controlling plateis used in a manufacturing method according to the first embodiment.

FIG. 7 is a graph showing distribution of particle sizes of the fineparticles obtained in the method of manufacturing fine particlesaccording to the first embodiment.

FIG. 8 is a view showing a constitution of an apparatus formanufacturing fine particles according to a second embodiment of thepresent invention.

FIG. 9 is a view showing a constitution of an apparatus formanufacturing fine particles according to a third embodiment of thepresent invention.

FIG. 10 is a view showing a constitution of an apparatus formanufacturing fine particles according to a fourth embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 4 is a constitutional view of an apparatus for manufacturing fineparticles according to a first embodiment. This apparatus formanufacturing fine particles includes a source gas inlet part 2 and acarrier gas inlet part 3 provided on one end of a reactor 1, and adiluting gas inlet part 4 provided on the other end. Moreover, in middleof a flow channel of a composite gas flow of the source gas and thecarrier gas (hereinafter referred to as a “reactive gas flow”) insidethe reactor 1, a gas-flow controlling plate 6 a is disposed almostperpendicularly with respect to the gas flow channel in the reactor 1for equalizing a flow rate of the reactive gas flow with respect to across section of the flow channel. Similarly, a gas-flow controllingplate 6 b is also disposed in the middle of a flow channel of a dilutinggas flow for equalizing a flow rate of the inert gas flow with respectto a cross section of the flow channel.

The gas-flow controlling plate 6 (6 a or 6 b) is typically aheat-resistive plate made of metal or ceramics provided with a pluralityof through-holes. To be more precise, various examples of the gas-flowcontrolling plates are illustrated in FIG. 5A to FIG. 5D. On a gas-flowcontrolling plate 61 shown in FIG. 5A, a plurality of pin holes 62 areuniformly formed with intervals of several millimeters on a plate madeof metal or ceramics. Although the size of the gas-flow controllingplate 61 and the size and the number of the pin holes 62 depend on thesize of the reactor 1, the gas flow rates or the like, the gas-flowcontrolling plate 61 is also designed to satisfy a condition forequalizing the flow rate of the gas flow passing through the gas-flowcontrolling plate 6 with respect to the cross section of the flowchannel. For example, the size of the pin holes (through-holes) 62 isset in a range from about 0.1 to 0.5 mmφ, so that the flow rate of thegas flow thus obtained is adjusted approximately to 100 cm/sec.

The gas-flow controlling plate 6 shown in FIG. 5B is a meshed plate 63such as a metallic wire mesh. Note that a single metallic wire mesh maybe used as the gas-flow controlling plate 6 as shown in FIG. 5B, or aplurality of metallic wire meshes may be stacked and used as thegas-flow controlling plate 6, alternatively.

Furthermore, as shown in FIG. 5C, a plate 64 composed of a bundle ofheat-resistive metallic or ceramic tubes may be also used as thegas-flow controlling plate 6. In this case, the tubes should be disposedparallel to the gas flow. Lengths or sizes of the respective tubes mayvary as long as the gas-flow controlling plate 6 can satisfy a conditionfor equalizing the flow rate of the gas flow passing through thegas-flow controlling plate 6 with respect to the cross section of theflow channel. Otherwise, it is also possible to use a metallic orceramic carrier having a plurality of honeycomb cavities as the gas-flowcontrolling plate 6.

It should be noted that the respective small through-holes to be formedon the gas-flow controlling plates 6 do not have to be formed entirelyinto the same size or the same shape. In general, the gas flow reachingthe gas-flow controlling plate 6 tends to show a faster flow rate in thecenter of the flow channel and a slower flow rate in the peripherythereof. Accordingly, with a plate 65 as shown in FIG. 5D, the flow rateof the gas flow with respect to the cross section of the flow channelcan be equalized more easily if the sizes of the small through-holes ina central portion are made larger and the sizes of the smallthrough-holes in a peripheral portion are made gradually smalleroutward.

It is not necessary to use the same type for the two gas-flowcontrolling plates 6 a and 6 b. In other words, materials or shapes ofthe gas-flow controlling plates 6 a and 6 b can be independentlyselected as appropriate for each plate.

A distance between the two gas-flow controlling plates 6 a and 6 b isset in a range from 5 cm to 20 cm, more preferably to about 10 cm, forexample, so that the reactive gas flow and the diluting gas flow can bemerged while maintaining the respective flow rates after rectification.

The gas exhaust port 7 is disposed on a wall of the reactor in a regionwhere the reactive gas flow and the diluting gas flow are merged. Thedischarged gas containing the fine particles is transferred via acooling device 8 to a fine particle collector 9 for collecting andpreserving fine particles. The fine particle collector 9 is filled witha solution of water, methanol or the like, which contains a surfactantsuch as a fatty acid salt. Accordingly, only the fine particles arecollected while the discharged gas passing through them, and the rest ofthe gas is discharged to the atmosphere. A surfactant includes moleculeseach composed of a hydrophilic group which tends to link water, and alipophilic group (also referred to as a hydrophobic group) which tendsto link oil. Therefore, a surface of each fine particle caught by thesolution is covered with the surfactant, thus the fine particles areprevented from cohesion and stored in the fluid while maintaining adispersed state.

Although the size and the shape of the reactor are not particularlylimited, it is possible to use a cylindrical reactor applicable to a CVDapparatus for 8-inch wafers.

Moreover, provision of the gas exhaust port 7 is not necessarily limitedto one location. Instead, two or more gas exhaust ports may be providedas shown in FIG. 4. As the exhaust ports are provided more, the reactivegas flow and the diluting gas flow after merging can be discharged moresmoothly. When the gas exhaust ports 7 are provided in pluralities, thecooling device 8 and the fine particle collector 9 may be providedseverally on each gas exhaust port. Alternatively, the plurality of gasexhaust ports 7 may be joined to one common pipe, and the pipe may beconnected to a common cooling device 8 and to a common fine particlecollector 9.

Now, description will be made with reference to FIG. 4 regarding amethod of manufacturing fine particles according to the first embodimentby use of the above-described apparatus for manufacturing fineparticles. Specifically, a method of manufacturing ZnS fine particles,which are usable as fluorescent materials, will be described as anexample.

Zn(CH₃)₂ and H₂S are used as the source gas, for example. As for thecarrier gas for the source gas, inert gas such as nitrogen can be used.Moreover, the inert gas such as nitrogen can be also used as thediluting gas. Each gas is preserved in a dedicated tank (not shown).

First, the inert gas as the carrier gas is introduced into the reactor 1from the carrier gas inlet part 3, and the inert gas as the diluting gasis introduced into the reactor 1 from the diluting gas inlet part 4.These gases constitute a gas flow toward the exhaust ports 7.

Here, it is preferable that the amounts of the flow of the two types ofthe introduced gas are controlled to be almost equal. The carrier gasflow and the diluting gas flow introduced are controlled by the gas-flowcontrolling plates 6 a and 6 b to have the uniform flow rates withrespect to the cross section of the flow channel respectively. Then, thecarrier gas flow and the diluting gas flow are collided and mergedalmost in the center of the space between the gas-flow controlling plate6 a and the gas-flow controlling plate 6 b. Thereafter, the merged gasis discharged from the adjacent gas exhaust ports 7 smoothly.Accordingly, occurrence of a turbulent flow caused by the collision ofthe gas flows hardly affects the surrounding.

Next, the inside of the reactor 1 is heated up to a range from 600° C.to 700° C. with the heater 5 and the pressure inside the reactor 1 isset to 1.013×10⁵ Pa (760 torr). While, the temperature of the coolingdevice 7 is set to a room temperature and the pressure thereof is set to1.013×10⁵ Pa (760 torr) as similar to the inside of the reactor 1.

When the gas flows and the temperature inside the reactor 1 becomestable, the source gas containing Zn(CH₃)₂ gas and H₂S gas is introducedfrom the source gas inlet part 2 into the reactor 1. The source gas flowconstitutes the reactive gas flow together with the carrier gas alreadyflowing, and the reactive gas flow flows inside the reactor 1.

The source gas introduced into the reactor 1 is heated up to the rangefrom 600° C. to 700° C. in the process of passing through a portionwhere the heater 5 is provided, thus the source gas causes a pyrolyticreaction as shown in the following chemical formula (FII) and generatessolid ZnS molecules. Such ZnS molecules become ZnS fine particle cores.Zn(CH₃)₂+H₂S→ZnS (solid)+2CH₄ (gas)  (FII)

The carrier gas and the source gas containing, i.e. the reactive gasflow containing the ZnS fine particles is controlled to have a uniformflow rate with respect to the cross section of the flow channel by useof the gas-flow controlling plate 6 a while proceeding with the fineparticle core generating reaction, and then the reactive gas flow mergeswith the diluting gas flow, which is similarly controlled to have auniform flow rate with respect to the cross section of the flow channel.When the two type gas flows are merged, the reactive gas is dilutedimmediately, thus, growth of the fine particles is stopped.

According to the conventional method, the growth of fine particlesinevitably proceeds with the “fine particle core generating process” ofthe first stage (I), the “fine particle cluster generating process” ofthe second stage (II) and the “cluster cohering process” of the thirdstage (III). Then, the growth of the fine particles is stopped bymerging with the diluting gas outside the reactor and the fine particlesare collected thereafter. On the contrary, according to the method ofmanufacturing fine particles according to the first embodiment, thereactive gas flow which is excited by heating merges with the dilutinggas flow which is counter-flow. Therefore, surfaces of the ZnS fineparticles in the reactive gas flow are covered with nitrogen in thediluting gas at a very early stage. Accordingly, clustering of the ZnSfine particles at the second stage (II) and cohesion of the clusters atthe third stage (III) are suppressed. Thus, the growth of the fineparticles will be stopped at the first stage (I) or in mid-course of thesecond stage (II). As a result, it is possible to suppress the growth ofthe fine particle sizes up to some 5 nm on the average.

Moreover, in the first embodiment, the reactive gas flow and thediluting gas flow are adjusted to the uniform flow rates with respect tothe cross section of the flow channel in the process of passing throughthe gas-flow controlling plates 6 a and 6 b respectively. Accordingly, atime interval for the reactive gas flow to merge with the diluting gasflow is equalized within the cross section of the gas flow channel. Thetime interval required for merger controls a time period for the growthof the fine particles. The fact that the time period for the growth ofthe fine particles becomes equal irrespective of the location refers tonothing else but capability of equalizing the sizes of the obtained fineparticles. Therefore, it is possible to uniform the sizes of theobtained fine particles.

The above-described effect of the gas-flow controlling plates 6 can beconceptually explained as follows. Here, assuming that the gas-flowcontrolling plates are infinitely large flat plates, consideration willbe made regarding the flows to be formed in the case that the two flatplates are disposed in a mutually facing manner and gas is emitted outof each flat plate. Note that the flow of the gas is assumed to be asteady-state laminar flow.

An equation for the flow refers to a formula of conservation of mass ina steady state (an equation of continuity) based on a cylindricalcoordinate system, which is expressed as:

$\begin{matrix}{{\frac{\partial u}{\partial r} + \frac{u}{r} + \frac{\partial w}{\partial z}} = 0} & ({f1})\end{matrix}$

Here, u and w refer to components of velocity in a radial direction andin an axial direction, respectively.

If the above-described equation is subjected to variable transformationusing functions g and f relevant only to the axial direction of the gasflow, then,

$\begin{matrix}{{{g(z)} = \frac{u}{r}},} & ({f2}) \\{{f(z)} = {- \frac{w}{2}}} & ({f3})\end{matrix}$are applicable. Accordingly, the equation of continuity can be expressedonly by using the component z of the axial direction of the gas flow,such as:

$\begin{matrix}{{g(z)} = \frac{\mathbb{d}{f(z)}}{\mathbb{d}z}} & ({f4})\end{matrix}$Meanwhile, equations of conservation of momentum are expressed by thefollowing formulae:

$\begin{matrix}{{{u\frac{\partial u}{\partial r}} + {w\frac{\partial u}{\partial z}}} = {{{- \frac{1}{\rho}}\frac{\partial p}{\partial r}} + {v\left( {\frac{\partial^{2}u}{\partial r^{2}} + {\frac{1}{r}\frac{\partial u}{\partial r}} - \frac{u}{r^{2}} + \frac{\partial^{2}u}{\partial z^{2}}} \right)}}} & ({f5}) \\{{{u\frac{\partial w}{\partial w}} + {w\frac{\partial w}{\partial z}}} = {{{- \frac{1}{\rho}}\frac{\partial p}{\partial z}} + {v\left( {\frac{\partial^{2}w}{\partial r^{2}} + {\frac{1}{r}\frac{\partial w}{\partial r}} + \frac{\partial^{2}w}{\partial z^{2}}} \right)}}} & ({f6})\end{matrix}$Here, ρ refers to density and ν refers to kinematic viscosity.

By applying the following constant, namely,

$\begin{matrix}{H = {{\frac{1}{r}\frac{\partial p}{\partial r}} = {constant}}} & ({f7})\end{matrix}$to these two equations of momentum, an ordinary differential equationusing only the parameter v is derived as follows:

$\begin{matrix}{{{vf}^{\prime''} - {2{ff}^{''}} + f^{\prime\; 2} + \frac{H}{p}} = 0} & ({f8})\end{matrix}$

Therefore, by resolving the above-mentioned formulae (f4), (f7) and(f8), it is possible to find the solutions g and f, which are notdependent on the radius. As a result, the component w of velocity in theaxial direction of the gas flow constitutes a constant valueirrespective of the radius. After all, it is possible to explainconceptually that the mode of mixture of the two gas flows, which arecollided and merged after passing through the gas-flow controllingplates, becomes uniform with respect to the cross section of the gasflow channel regardless of the location.

FIG. 6 is a graph showing temperatures in the merging region of the gaspassing through the gas-flow controlling plates 6 a and 6 b in the firstembodiment, which are obtained by simulation. The axis of ordinatesindicates the temperature and the axis of abscissas indicates thedistance from the gas-flow controlling plate 6 b, which is disposed inthe gas flow channel of the diluting gas. The graph plots a temperature(T1) variation on the central axis of the gas flow and a temperature(T2) variation in a position away from the central axis by 2 cm in theradial direction. Note that the simulations applies the condition inthat a distance between the two gas-flow controlling plates 6 a and 6 bis set to 5 cm and that the reactive gas heated up to 1000 K (727° C.)flows from top down and the diluting gas at 300 K (27° C.) flows frombottom up.

As shown in FIG. 6, the temperature (T1) on the central axis of the gasflow and the temperature (T2) in the position distant from the centralaxis by 2 cm in the radial direction are almost the same. Accordingly,it is learned that the mode of mixture of the two types of the gasseverally having the different temperatures are almost uniform in thedirection of the cross section of the flow channel. From this result, itis confirmed that a uniform reaction can be achieved regardless of theposition in the cross section of the flow channel. Although thetemperature of the gas drops sharply in the merging region (in theposition about 2 cm away from the gas-flow controlling plate 6 b), sucha region causing the sharp temperature change is limited to very narrowpart of the merging region. Accordingly, it is also learned that aninfluence of the turbulent flow caused by the merger of the gas ishardly diffusive. Such an effect of the gas-flow controlling plates issimilarly applicable to other embodiments to be described later.

The fine particles thus obtained are discharged from the gas exhaustports 7 together with the reactive gas and the diluting gas. Atemperature of the gas immediately after discharge is at 100° C. orthereabout. However, the gas is cooled down to a room temperature in thecourse of passing through the cooling devices 8. The discharged gascontaining the fine particles is further guided to the fine particlecollectors 9. When the discharged gas passes through a solution based ona solvent of ethanol, methanol or the like dissolving a surfactant, theZnS fine particles are collected and the rest of the discharged gas isdischarged to the atmosphere.

In this way, the ZnS fine particles are preserved within the solution inthe fine particle collector 9 in a dispersed state. When ZnS fineparticles are necessary, the ZnS fine particles can be obtained byheating and drying the solution preserved in the fine particle collector9.

FIG. 7 shows distribution particle sizes of the ZnS fine particles,which are manufactured by use of the method for manufacturing fineparticles according to the first embodiment. It is learned that therange of the distribution of particle sizes is narrower as compared tothe distribution of particle sizes obtained in accordance with theconventional manufacturing method, and that the fine particles withsizes of several nanometers are obtained intensively.

Although only about 30% of the total fine particles obtained by theconventional manufacturing method have the particle sizes within 5 nm,the fine particle having the particle sizes within 5 nm occupies 90% ormore in the total fine particles obtained by the manufacturing methodaccording to the first embodiment. Therefore, a process of furtherclassifying the fine particles collected is not required unlike theprior art.

The obtained ZnS particles with the particles sizes of severalnanometers exert quantum effects. Accordingly, if the ZnS particles areused in light-emitting elements such as LEDs, it is possible tomanufacture the light-emitting elements with high emission efficiency.

Note that the heater 5 is provided on an outside wall of the reactor inthe apparatus for manufacturing fine particles of the first embodiment.Here, it is preferable that the heater 5 is provided only on the outsidewall of the reactor 1 in the vicinity of the central portion thereof. Ifthe heater 5 is provided in the vicinity of the source gas inlet part 2or the carrier gas inlet part 4, the fine particles generated by thegenerating reaction tend to adhere to the vicinities of the respectiveinlet parts. Accordingly, there is a risk that the fine particles closethe respective inlet parts after continuous use. In the meantime, it isalso preferred to shorten the interval from the time of thermalexcitation of the reactive gas flow with the heater 5 to the time whenthe reactive gas flow and the diluting gas flow are merged, in terms ofavoiding overgrowth of the generated particles.

In the above-described condition, the temperature of the reactive gasflow is set in the range from 600° C. to 700° C. However, it is alsopossible to conduct the reaction in a wider temperature range, such as arange from 100° C. to 1000° C. When the temperature is set higher, thespeed of growth of the fine particles becomes faster, therefore, theparticle sizes of the obtained fine particles become slightly larger. Onthe contrary, when the temperature is set lower, the speed of growth ofthe fine particles becomes slower, whereby the particle sizes of theobtained fine particles become smaller.

Moreover, in the above-described condition, the pressure inside thereactor is set to 1.013×10⁵ Pa (760 torr). However, it is also possibleto use the reactor in a pressure range from 1.33×1.0³ Pa to 1.013×10⁵ Pa(10 to 760 torr). When the pressure is set lower, the speed of growth ofthe fine particles becomes slower, whereby the particles sizes of theobtained fine particulars become smaller. In addition, when the pressureinside the reactor is set lower, it is also possible to prevent theoccurrence of undesired mixed flow due to a thermal convection caused bythe heated gas and the diluting gas.

Moreover, although just one pipe is described above as an example of thesource gas inlet part 2, it is also possible to provide a plurality ofsource gas inlet parts.

As for surfactants and the like to be contained in the solution filledin the fine particle collector 9, there are cited various surfactantssuch as anionic surfactants (fatty acid salts, alkyl sulfates, acidesters, polyoxyethylene, alkyl ethers, sulfuric acid esters,alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkylsulfosuccinates, alkyl diphenylether disulfonates, alkyl phosphates andother anionic surfactants, naphthalene sulfuric acid formaldehydecondensates, and special polycarboxylic type high polymer surfactants),nonionic surfactants (surfactants containing long-chain alkyls such aspolyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers,polyoxyethylene derivatives, sorbitan fatty acid esters, polyoxyethylenesorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters,glycerol fatty acid esters, polyoxyethylene fatty acid esters,polyoxyethylene alkyl amines, alkyl alkanol amides, trioctylphosphineoxide, dodecylamines and alkanthiols, and other nonionic surfactants),cationic surfactants (alkyl amine salts, quaternary ammonium salts, andother cationic surfactants), amphoteric surfactants (alkyl betaines,amine oxides, and other amphoteric surfactants), and other surfacemodification agents.

As described above, in the case of using the method of manufacturingfine particles according to the first embodiment, the source gas isexcited by heating so as to initiate growth of the fine particles, andthen the growth of fine particle is stopped immediately after the mergerwith the diluting gas. Accordingly, it is possible to shorten the timeperiod of the fine particle generating reaction and thereby suppressincreases in particle sizes due to cohesion. Moreover, the reactive gasflow and the diluting gas flow are merged after the flow rates of therespective gas flows are equalized with respect to the cross section ofthe flow channel. Accordingly, it is possible to equalize the timeperiod from initiation to termination of the fine particle generatingreaction on the cross section of the flow channel. Therefore, the rangeof distribution of the particle sizes of the obtained fine particles canbe narrowed. Thus, it is possible to obtain the fine particles in evensizes within 10 nm suitable for exerting the quantum effects, and theclassification process is not required unlike the prior art. As aresult, it is possible to improve raw material efficiency of the sourcegas and to reduce the manufacturing costs.

Second Embodiment

FIG. 8 shows a constitutional view of an apparatus for manufacturingfine particles according to a second embodiment. The apparatus formanufacturing fine particles of the second embodiment has a constitutionsubstantially similar to the apparatus for manufacturing fine particlesaccording to the first embodiment. However, a large difference is thatthe apparatus according to the second embodiment includes aplasma-generating power source 10 as a source gas excitation device.

Specifically, the apparatus for manufacturing fine particles accordingto the second embodiment also includes a source gas inlet part 2 and acarrier gas inlet part 3 provided on one end of a reactor 1, a dilutinggas inlet part 4 provided on the other end counter-flow thereto.Gas-flow controlling plates 6 c and 6 d provided in the middle of a flowchannel of a reactive gas flow composed of the source gas and thecarrier gas and the middle of a diluting gas flow for equalizing flowrates of the gas flow with respect to a cross section of the flowchannel respectively. Moreover, the gas-flow controlling plates 6 c and6 d are made of metallic plates so as to function also as counterelectrodes for generating plasma inside the reactor 1. One of thegas-flow controlling plates is connected to the plasma-generating powersource 10. The plasma is generated in a region where the reactive gasflow and the diluting gas flow are merged. Note that it is also possibleto provide discrete counter electrodes required for generation of theplasma on upper and lower sides independently of the gas-flowcontrolling plates 6 c and 6 d.

Moreover, gas exhaust ports 7 are provided on a wall of the reactor 1 ina gas merging region, and each pipe on the gas exhaust port 7 is drawnout to a fine particle collector 9 via a cooling device 8.

Now, description will be made with reference to FIG. 8 regarding amethod of manufacturing fine particles according to the secondembodiment by use of the above-described apparatus for manufacturingfine particles. A method of manufacturing ZnS fine particles, which areusable as fluorescent materials, will be described as an example. Thecarrier gas and the diluting gas for use in this embodiment are similarto those used in the first embodiment.

First, inert gas as the carrier gas is introduced into the reactor 1from the carrier gas inlet part 3, and inert gas as the diluting gas isintroduced into the reactor 1 from the diluting gas inlet part 4. Thesegases constitute a gas flow toward the exhaust ports 7. Such a gas flowfurther flows to the cooling devices 8 and to the fine particlecollectors 9.

Next, the pressure inside the reactor 1 is set in a range from 1.33×10²to 6.67×10³ Pa (1 to 50 torr), preferably at 1.33×10² Pa. The gaspressure inside each of the cooling devices 8 is set to the samepressure as the pressure inside the reactor. Thereafter, the plasma isgenerated inside the reactor 1 by use of the plasma-generating powersource 10. Moreover, the temperature in the plasma-generating region isset in a range from 400° C. to 500° C. by use of a heater (not shown).

Subsequently, the source gas containing Zn(NO₃)₂ and SC(NH₂)₂ isintroduced into the reactor 1. The introduced source gas constitutes thereactive gas flow together with the carrier gas and passes through thegas-flow controlling plate 6 c. After a flow rate of the reactive gasflow is equalized with respect to the cross section of the flow channel,the reactive gas flow further flows into the plasma-generating region.Here, a plasma reaction as expressed by the following formula (FIII)takes place, whereby the respective ingredients of the source gas areexcited for generating ZnS molecules. Such ZnS molecules constitute ZnSfine particle cores.Zn(NO₃)₂+SC(NH₂)₂+e (electron)→ZnS (solid)+NO₂ (gas)+CO₂ (gas)+(NH₂)2(gas)+e (electron)  (FIII)

Meanwhile, a nitrogen gas flow as the diluting gas, which is adjusted toa gas flow with a uniform flow rate with respect to the cross section ofthe flow channel, flows into the plasma-generating region and merge withthe reactive gas flow. As the diluting gas covers surfaces of thegenerated ZnS particles, further growth of the fine particles isstopped.

As described above, according to the method of manufacturing fineparticles of the second embodiment, the growth of the fine particles isstopped by the diluting gas immediately after the reaction caused by theplasma excitation. Accordingly, the growth of the fine particles issurely stopped in the “fine particle core generating process” of thefirst stage (I) or in mid-course of the “fine particle clustergenerating process” of the second stage (II). As a result, it ispossible to suppress the growth of the fine particle sizes up to some 3nm on the average.

In addition, according to the second embodiment as well, the flow ratesof the reactive gas flow and the diluting gas flow are equalizedseverally with respect to the cross section of the flow channel in thecourse of passing through the gas-flow controlling plates 6 c and 6 d.Therefore, a time period until merger of the reactive gas and thediluting gas is equalized at any location on the cross section of theflow channel. Since the time interval from start to end of the fineparticle generating reaction is equalized in terms of the direction ofthe cross section of the flow channel, it is thereby possible toequalize sizes of the obtained fine particles.

The fine particles thus obtained are discharged from the gas exhaustports 7 together with the reactive gas and the diluting gas. Atemperature of the gas immediately after discharge is at 100° C. orthereabout. However, the gas is cooled down to a room temperature in thecourse of passing through the cooling devices 8.

The discharged gas containing the fine particles is further guided to asolution containing a surfactant filled in the fine particle collector9, whereby the ZnS fine particles are collected by the solution and therest of the discharged gas is discharged to the atmosphere.

In this way, the ZnS fine particles are preserved within the solution inthe fine particle collector 9 in a dispersed state. When ZnS fineparticles are necessary, the ZnS fine particles can be obtained byheating and drying the solution preserved in the fine particle collector9.

As described above, in the case of using the method of manufacturingfine particles according to the second embodiment, the source gas isexcited by plasma and thereby causes the reaction for generating thefine particles in the merging region of the reactive gas flow and thediluting gas flow, and then the growth of the fine particles is stoppedby the diluting gas. Accordingly, it is possible to generate the fineparticles even finer than the case where the method of manufacturingfine particles according to the first embodiment is used. Therefore, itis possible to obtain the fine particles in even sizes suitable forexerting the quantum effects, and the classification process is notrequired unlike the prior art. As a result, it is possible to improveraw material efficiency of the source gas and to reduce themanufacturing costs. Moreover, according to the second embodiment, thesource gas is excited by plasma after the source gas passes through thegas-flow controlling plate 6 c. Accordingly, there is no risk thatthrough-holes on the gas-flow controlling plate 6 c are clogged by thegenerated fine particles.

Third Embodiment

FIG. 9 shows a constitutional view of an apparatus for manufacturingfine particles according to a third embodiment. The apparatus formanufacturing fine particles of the third embodiment also has aconstitution substantially similar to the apparatus for manufacturingfine particles according to the first embodiment. However, a largedifference is that a heater is not provided on a source gas inlet partside of a reactor 1 but a heater 5 b is provided on a diluting gas inletpart side instead.

Specifically, the apparatus for manufacturing fine particles accordingto the third embodiment also includes a source gas inlet part 2 and acarrier gas inlet part 3 provided on one end of a reactor 1, and adiluting gas inlet part 4 provided on the other end counter-flowthereto. The apparatus also includes gas-flow controlling plates 6 e and6 f severally provided in the middle of a flow channel of a reactive gasflow composed of the source gas and the carrier gas and in the middle ofa diluting gas flow for equalizing flow rates of the reactive gas flowwith respect to a cross section of the flow channel.

The heater 5 b is disposed on an outside wall of the reactor 1 in aspace between the diluting gas inlet part 4 and the gas-flow controllingplate 6 f. Gas exhaust ports 7 are provided on a wall of the reactor ina region where the reactive gas flow and the diluting gas flow aremerged. Pipes are provided so as to conduct discharged gas toward fineparticle collectors 9 via cooling devices 8 for cooling the dischargedgas containing fine particles.

Now, description will be made with reference to FIG. 9 regarding amethod of manufacturing fine particles according to the third embodimentby use of the above-described apparatus for manufacturing fineparticles. As similar to the first and the second embodiments, themethod of manufacturing ZnS fine particles, which are usable asfluorescent materials, will be described as an example. The source gas,the carrier gas and the diluting gas for use in this embodiment aresimilar to those used in the first embodiment.

First, as similar to the first and the second embodiments, inert gas asthe carrier gas is introduced into the reactor 1 from the carrier gasinlet part 3, and inert gas as the diluting gas is introduced into thereactor 1 from the diluting gas inlet part 4. These introduced gasesconstitute a gas flow toward the gas exhaust ports 7. This gas flowfurther flows to the cooling devices 8 and to the fine particlecollector 9.

Next, the inert gas introduced from the diluting gas inlet part 4 isheated up to a temperature in a range from 600° C. to 700° C. and thegas pressure inside the reactor 1 is set to 9.33×10⁴ Pa (700 torr). Thetemperature inside each of the cooling devices 8 is set to a roomtemperature and the pressure therein is set to the same pressure as thepressure inside the reactor.

Thereafter, the source gas containing Zn(CH₃)₂ gas and H₂S gas isintroduced from the source gas inlet part 2 into the reactor 1. Theintroduced source gas constitutes the reactive gas flow together withthe carrier gas. The reactive gas flow passes through the gas-flowcontrolling plate 6 e, whereby the reactive gas flow is adjusted to agas flow with a flow rate being equalized with respect to a crosssection of a flow channel. On the other hand, the diluting gas isintroduced from the diluting gas inlet part 4 into the reactor and thenheated up to the range from 600° C. to 700° C. with the heater 5 b. Thediluting gas thus heated is further adjusted to a gas flow with a flowrate being equalized with respect to the cross section of the flowchannel by use of the gas-flow controlling plate 6 f.

Thereafter, the reactive gas flow and the heated diluting gas flow arecollided and merged. The source gas in the source gas flow is heated andexcited by the heat in the diluting gas flow, whereby the source gascauses the following reaction as shown in the chemical formula (FII) assimilar to the first embodiment and generates solid ZnS molecules.Zn(CH₃)₂+H₂S→ZnS (solid)+2CH₄ (gas)  (FII)

Nevertheless, the generated ZnS fine particles are surrounded by thediluting gas simultaneously with generation. Therefore, generation ofZnS fine particle cores is immediately stopped. Accordingly, the growthof the fine particles is more surely stopped in the “fine particle coregenerating process” of the first stage (I) or in mid-course of the “fineparticle cluster generating process” of the second stage (II). As aresult, it is possible to suppress the growth of the fine particle sizesup to some 3 nm on the average.

Moreover, also in the third embodiment, since the reactive gas flow andthe diluting gas flow are adjusted severally to have the equalized flowrates with respect to the cross section of the flow channel in theprocess of passing through the gas-flow controlling plates 6 e and 6 f,a time interval for the reactive gas flow to merge with the diluting gasflow is equalized irrespective of the location, whereby sizes of theobtained fine particles can be equalized. As a result, it is possible touniform the sizes of the obtained fine particles.

The fine particles thus obtained are discharged from the gas exhaustports 7 together with the reactive gas and the diluting gas. Thedischarged gas is cooled down to a room temperature with the coolingdevices 8. Furthermore, the discharged gas is guided to a solutioncontaining a surfactant filled in the fine particle collector 9. The ZnSfine particles are collected by the solution in the course oftransmission through the solution and the rest of the discharged gas isdischarged to the atmosphere.

In this way, the ZnS fine particles are preserved within the solution inthe fine particle collector 9 in a dispersed state. When ZnS fineparticles are necessary, the ZnS fine particles can be obtained byheating and drying the solution preserved in the fine particle collector9.

As described above, in the case of using the method of manufacturingfine particles according to the third embodiment, the source gas isheated and excited in the merging region of the reactive gas flow andthe diluting gas flow, whereby growth of the fine particles is initiatedbut stopped almost simultaneously due to the diluting gas. Accordingly,it is possible to generate the fine particles even finer than the casewhere the method of manufacturing fine particles according to the firstembodiment is used. Therefore, it is possible to obtain the fineparticles with uniform particles in nanometer sizes suitable forexerting the quantum effects, and the classification process is notrequired unlike the prior art. As a result, it is possible to improveraw material efficiency of the source gas and to reduce themanufacturing costs. Moreover, according to the third embodiment, thesource gas is heated and excited after the source gas passes through thegas-flow controlling plate 6 e. Accordingly, there is no risk thatthrough-holes on the gas-flow controlling plate 6 e are clogged by thegenerated fine particles.

Fourth Embodiment

A method of manufacturing fine particles according to a fourthembodiment is characterized in that oxygen-containing gas is used asdiluting gas. In this method, generation of fine particle cores ispromoted by an oxidation (burning) reaction of source gas. Accordingly,source gas exciting means such as a heater or a plasma generator is notrequired therein. Therefore, it is possible to use an apparatus as shownin FIG. 10, which is equivalent to the apparatus according to the firstembodiment or the apparatus according to the third embodiment but theheater is removed therefrom.

Fine particles to be manufactured according to this method are mainlyoxides, which include oxide fluorescent materials such as Y₂O₅, andpowder for cosmetic use such as TiO₂. In the case of manufacturing Y₂O₅,the following method is applicable.

First, as similar to the first embodiment, inert gas as carrier gas isintroduced into a reactor 1 from a carrier gas inlet part 3, and eitheroxygen gas or nitrogen gas mixed with oxygen gas as the diluting gas isintroduced into the reactor 1 from a diluting gas inlet part 4. Theseintroduced gases constitute a gas flow toward gas exhaust ports 7. Sucha gas flow further flows to cooling devices 8 and to fine particlecollectors 9.

Next, the gas pressure inside the reactor 1 is set to 1.013×10⁵ Pa (760torr) or less. Moreover, the temperature inside each of the coolingdevices 8 is set to a room temperature and the pressure therein is setto almost the same pressure as the pressure inside the reactor 1.

Thereafter, yttrium acetylacetate (Y(C₅H₇O₂)₃) as the source gas isintroduced from a source gas inlet part 2 into the reactor 1. Theintroduced source gas constitutes a reactive gas flow together with thecarrier gas. The reactive gas flow passes through a gas-flow controllingplate 6 g, whereby the reactive gas flow is adjusted to a gas flow witha flow rate being equalized with respect to a cross section of a flowchannel. On the other hand, the diluting gas containing oxygen isintroduced from the diluting gas inlet part 4 into the reactor 1 andthen adjusted to a gas flow with a flow rate being equalized withrespect to the cross section of the flow channel by use of a gas-flowcontrolling plate 6 h.

In a merging region where the reactive gas flow and the diluting gasflow are merged, the source gas and oxygen causes a drastic oxidation(burning) reaction as expressed in the following formula (FIV), wherebyY₂O₅ fine particle cores are generated.aY(C₅H₇O₂)₃ +bO₂→Y₂O₅ (solid)+CO₂ (gas)+H₂O  (FIV)

Meanwhile, the Y₂O₅ fine particles thus generated are surrounded by thediluting gas almost simultaneously with the oxidation (burning)reaction. Therefore, growth of the Y₂O₅ fine particle cores is stoppedin that state. Accordingly, the growth of the fine particles is moresurely stopped in the “fine particle core generating process” of thefirst stage (I) or in mid-course of the “fine particle clustergenerating process” of the second stage (II). As a result, it ispossible to suppress the growth of the fine particle sizes up to some 3nm on the average.

Moreover, also in the fourth embodiment, since the reactive gas flow andthe diluting gas flow are adjusted severally to have the equalized flowrates with respect to the cross section of the flow channel in theprocess of passing through the gas-flow controlling plates 6 g and 6 h,a time interval for the reactive gas flow to merge with the diluting gasflow is equalized irrespective of the location, whereby sizes of theobtained fine particles can be equalized. As a result, it is possible touniform the sizes of the obtained fine particles.

The fine particles thus obtained are discharged from the gas exhaustports 7 together with the reactive gas and the diluting gas. Thedischarged gas is cooled down to a room temperature with the coolingdevices 8. Furthermore, the discharged gas is guided to a solutioncontaining a surfactant filled in the fine particle collector 9, thus,the Y₂O₅ fine particles are collected by the solution in the course oftransmission through the solution and the rest of the discharged gas isdischarged to the atmosphere.

As described above, in the case of using the method of manufacturingfine particles according to the fourth embodiment, the source gas causesthe oxidation (burning) reaction upon merging with the oxygen gascontained the diluting gas, whereby, the Y₂O₅ fine particle cores aregenerated. Moreover, the growth of the fine particles is stopped almostsimultaneously due to the diluting gas. Accordingly, it is possible togenerate the fine particles even finer than the case where the method ofmanufacturing fine particles according to the first embodiment is used.Since the fine particles with uniform particles in nanometer sizes canbe obtained, the classification process is not required unlike the priorart. As a result, it is possible to improve raw material efficiency ofthe source gas and to reduce the manufacturing costs.

Moreover, according to the fourth embodiment, the source gas merges withthe diluting gas containing oxygen after the source gas passes throughthe gas-flow controlling plate 6 g. Accordingly, there is no risk thatthrough-holes on the gas-flow controlling plate 6 g are clogged by thegenerated fine particles. Furthermore, since the fourth embodiment doesnot require a heater or a plasma-generating power source or the like forexciting the source gas, it is possible to save the costs of theapparatus.

In the case of manufacturing TiO₂ fine particles by use of themanufacturing method of the fourth embodiment, titaniumtetraisopropoxide, for example, may be used as the source gas and anoxidation (burning) reaction with oxygen may be promoted as follows:Ti(C₃H₈O)₄+19O₂→TiO₂ (solid)+12CO₂ (gas)+16H₂O  (FV)

The TiO₂ fine particles in the nanometer scale thus obtained have highspecific surfaces. Accordingly, if the TiO₂ fine particles are used asmaterials for a solar battery, the fine particles can absorb energy oflight efficiently. Therefore, it is possible to obtain a solar batterywith high power generation efficiency.

Other Embodiments

In the above-described first to fourth embodiments, gaseous materials atnormal temperatures are used for the fine particle source materials andintroduced into the reactor as the source gas. However, the fineparticle source materials are not limited to the gaseous materials, butliquid materials and solid materials are also applicable.

For example, when a liquid fine particle source material is used, theliquid fine particle source material may be atomized and introduced intothe reactor. Alternatively, it is also possible to heat and vaporize aliquid or solid fine particle source material, so that the vaporizedmaterial is introduced into the reactor.

Furthermore, it is also possible to prepare a solution, in which a gas,liquid or solid fine particle source material is dissolved in a solvent,and to atomize the solution for introduction into the reactor. Forexample, if particle source material atomized and introduced is excitedby heating with the apparatus according to the first embodiment, thefine particle source material inside the solution initiates a reactionto generate fine particles, simultaneously, the solvent around theparticles is gradually evaporated and removed from the ZnS particles.While the fine particles are surrounded by the solvent, the fineparticles are suppressed to be bonded or cohered together because thefine particles are prevented from contacting with one another by thesolvent. As the growth of the fine particle sizes can be delayedaccordingly, it is possible to form the sizes of the obtained particleseven smaller.

Although the present invention has been described with reference tocertain embodiments, it is needless to say that the present invention isnot limited only to the above-described embodiments and variousmodifications or alterations are applicable without departing from thespirit and scope of the invention.

For example, regarding types of fine particles to be fabricated, variousfine particles can be manufactured by use of a variety of source gas.For example, in addition to the ZnS as the fluorescent material, Y₂O₅and TiO₂, it is also possible to fabricate various magnetic materialsincluding metallic powder made of Co or Cr, ferrites, and the like. Arecording medium using magnetic fine particles in the nanometer scalefabricated in accordance with the above-described methods can achievesubstantially higher recording density.

Moreover, regarding the reactive apparatuses described in the respectiveembodiments, the mode of disposition of the reactor is not only limitedto a horizontal direction but it is also possible to dispose the reactorin a vertical direction. Furthermore, the carrier gas or the dilutinggas is not always limited to nitrogen, but other inert gas is alsoapplicable.

As described above, according to the first aspect of the method ofmanufacturing fine particles of the present invention, the fineparticles in the reactive gas flow are heated and then immediatelystopped to grow inside the reactor by merger with the diluting gasintroduced from the counter-flow direction. Therefore, it is possible toshorten the reactive time for generation of the fine particles andthereby to suppress the growth of the fine particles owing to cohesion.Moreover, the reactive gas flow and the diluting gas flow are severallyadjusted to the flow rates equalized with respect to the cross sectionof the flow channel prior to merger. Accordingly, it is possible toequalize the mode of mixture of the two types of gas in terms of thecross section of the flow passage. As a result, it is also possible toequalize the time interval from initiation to termination of the fineparticle generating reaction, which dominates the sizes of the fineparticles. Accordingly, it is possible to obtain the fine particles,which are uniform in nanometer sizes.

According to the second aspect of the method of manufacturing fineparticles of the present invention, the fine particle source materialsare excited and generation of the fine particles is thereby promoted inthe merging region of the reactive gas flow and the diluting gas flow,and the growth of the fine particles is stopped by dilution due to thediluting gas flow. Therefore, the growth of the fine particles isstopped immediately after initiation of the growth of the fineparticles. Accordingly, it is possible to set the time for the growth ofthe fine particles to a very short time period. Therefore, it ispossible to suppress increases in sizes of the fine particles due tobond or cohesion, whereby the fine particles in nanometer sizes can begenerated.

According to the first aspect of the apparatus for manufacturing fineparticles of the present invention, the apparatus can stop growth of thefine particles immediately after exciting the fine particle sourcematerials contained in the reactive gas flow by means of merger with thediluting gas inside the reactor. Therefore, it is possible to shortenthe time for the growth of the fine particles and to suppress increasesin sizes of the fine particles due to cohesion. Moreover, the reactivegas flow and the diluting gas flow are merged together after therespective gas flows are set to the flow rates equalized with respect tothe cross section of the flow channel by use of the first plate and thesecond plate severally provided with through-holes. Accordingly, it ispossible to equalize a mixing condition of the reactive gas flow and thediluting gas flow in terms of the cross section of the flow channel.Therefore, the time period from start to end of the fine particlegenerating reaction is equalized, whereby the fine particles can beobtained in uniform sizes.

According to the second aspect of the apparatus for manufacturing fineparticles of the present invention, the fine particle source materialsare excited by plasma and generation of the fine particles is therebypromoted in the merging region of the reactive gas flow and the dilutinggas flow, and the growth of the fine particles is stopped by dilutiondue to the diluting gas flow. Therefore, the virtual reactive time forgeneration of the fine particles can be substantially shortened.Accordingly, it is possible to suppress increases in sizes of the fineparticles due to bonding or cohesion, whereby the fine particles withinnanometer sizes can be obtained.

According to the third aspect of the apparatus for manufacturing fineparticles of the present invention, the diluting gas flow is heated andthen the fine particle source materials are heated in the merging regionof the reactive gas flow and the diluting gas flow with the heat of thediluting gas, whereby the fine particle cores are generated and thegrowth of the fine particles is stopped almost simultaneously bydilution due to the diluting gas flow. Therefore, the reactive time forgeneration of the fine particles can be substantially shortened.Accordingly, it is possible to suppress increases in sizes of the fineparticles due to bonding or cohesion, whereby the fine particles withinnanometer sizes can be obtained.

1. An apparatus for manufacturing fine particles, comprising: acylindrical reactor having a first end and a second end opposite to thefirst end; a first inlet part including at least one port introducing areactive gas flow containing a fine particle source material along anaxial direction of the reactor, the first inlet part being provided onthe first end of the reactor; a second inlet part including at least oneport introducing a diluting gas flow along the axial direction of thereactor, the second inlet part being provided on the second end of thereactor approximately counter-flow to the first inlet part; a heaterexciting the fine particle source material contained in the reactive gasflow; a first plate including through-holes which substantially equalizea flow rate of the reactive gas flow with respect to a cross section ofa flow channel, the first plate being disposed inside the reactor almostperpendicularly with the axial direction of the reactor; a second platefacing to the first plate, including through-holes which substantiallyequalize a flow rate of the diluting gas flow with respect to a crosssection of a flow channel, the second plate being disposed inside thereactor almost perpendicularly with respect to the axial direction ofthe reactor; a gas exhaust port provided in a merging region where thereactive gas flow passed through the first plate and the diluting gasflow passed through the second plate are merged; and a collector whichcollects fine particles contained in gas discharged from the gas exhaustport.
 2. The apparatus of claim 1, wherein the first plate and thesecond plate have a plurality of through-holes and sizes thereof are setfrom 0.1 to 0.5 mm.
 3. The apparatus of claim 1, wherein at least one ofthe first plate and the second plate is composed of a bundle of tubes.4. The apparatus of claim 1, wherein the first plate and the secondplate have a plurality of through-holes and sizes of a central portionof the through-holes are larger than sizes of a peripheral portion. 5.The apparatus of claim 1, wherein the collector includes a solutionincluding a surfactant.
 6. An apparatus for manufacturing fine particlescomprising: a cylindrical reactor having a first end and a second endopposite to the first end; a first inlet part including at least oneport introducing a reactive gas flow containing a fine particle sourcematerial along an axial direction of the reactor, the first inlet partbeing provided on the first end of the reactor; a second inlet partincluding at least one port introducing a diluting gas flow along theaxial direction of the reactor, the second inlet part being provided onthe second end of the reactor approximately counter-flow to the firstinlet part; a plasma generator which generates plasma in a mergingregion where the reactive gas flow and the diluting gas flow are merged;a gas exhaust port provided adjacently to the merging region; acollector which collects fine particles contained in gas discharged fromthe gas exhaust port; a first plate including through-holes whichsubstantially equalize a flow rate of the reactive gas flow with respectto a cross section of a flow channel, the first plate being disposedinside the reactor almost perpendicularly with respect to the axialdirection of the reactor; and a second plate facing to the first plate,including though-holes which substantially equalize a flow rate of thediluting gas flow with respect to a cross section of a flow channel, thesecond plate being disposed inside the reactor almost perpendicularlywith respect to the axial direction of the reactor.
 7. The apparatus ofclaim 6, wherein at least any one of the first plate and the secondplate constitutes an electrode of a plasma generating source.
 8. Anapparatus for manufacturing fine particles comprising: a cylindricalreactor having a first end and a second end opposite to the first end; afirst inlet part including at least one port introducing a reactive gasflow containing a fine particle source material along an axial directionof the reactor, the first inlet part being provided on the first end ofthe reactor; a second inlet part including at least one port introducinga diluting gas flow along the axial direction of the reactor, the secondinlet part being provided on the second end in the reactor approximatelycounter-flow to the first inlet part; a heater which heats the dilutinggas flow; a gas exhaust port provided in a merging region where thereactive gas flow and the diluting gas flow are merged; a collectorwhich collects fine particles contained in gas discharged from the gasexhaust port; a first plate including through-holes which substantiallyequalize a flow rate of the reactive gas flow with respect to a crosssection of a flow channel, the first plate being disposed inside thereactor almost perpendicularly with respect to the axial direction ofthe reactor; and a second plate facing to the first plate, includingthrough-holes which substantially equalize a flow rate of the dilutinggas flow with respect to a cross section of a flow channel, the secondplate being disposed inside the reactor almost perpendicularly withrespect to the axial direction of the reactor.